Meltflow stabilization of polyolefins

ABSTRACT

A method of incorporating a polymer melt flow stabilizer into a polymer by absorbing the stabilizer in a porous absorbent and incorporating the stabilizer-containing absorbent in the polymer.

United States Patent Mills MELT FLOW STABILIZATION OF POLYOLEFINSKenneth R. Mills, Bartlesville, Okla.

Phillips Petroleum Company Dec. 4, 1969 Inventor:

Assignee:

Filed:

Appl. No.:

US. Cl. ..260/4l A, 260/4l R, 260/45.7 S,

Int. Cl ..C08I 45/04, C08f 45/56 Field of Search ..260/4l 45.7 SU, 45.9,94.9 GB, 260/94.9 GD, DIG. 33

[ Feb. 22, 1972 Primary Examiner-Morris Liebman Assistant Examiner-J. H.Derrington Attorney-Young and Quigg [57] ABSTRACT A method ofincorporating a polymer melt flow stabilizer into a polymer by absorbingthe stabilizer in a porous absorbent and incorporating thestabilizer-containing absorbent in the polymer.

10 Claims, No Drawings MELT FLOW STABILIZATION F POLYOLEFINS Thisinvention relates to the processing of polyolefins.

In one of its more specific aspects, this invention relates to a methodof preventing a decrease in the melt-index value of polyolefins duringprocessing.

The processing of polyolefins such as polypropylene and polyethylene andsimilar polymeric compounds is well known. Such processing frequentlyinvolves heating the polymer to a temperature at which it becomes moltenand shaping the molten polymer by a thermoforming process such asextruding and injection, or blow molding. At molten temperatures,however, such polymers tend to decrease in melt flow and melt index,this decrease being known as melt index or melt flow dropoff. A decreasein melt flow, melt flow being the amount of polymer forcible through anorifice in a given time under a given load at a given temperature,indicates that the processing has altered the flow characteristics ofthe polymer from that desired value possessed by the polymer whenproduced.

The method of this invention provides a solution to such processingproblems.

According to this invention there is provided a method for introducingpolymer melt flow stabilizers into polymers which comprises adsorbingthe melt flow. stabilizer in a solid adsorbent and incorporating thesolid adsorbent containing the melt flow stabilizer into the polymer.

Accordingly, it is an object of this invention to provide improvedpolymers.

lt is another object of this invention to provide a method of melt flowstabilization of polyolefins which is of greater effect per quantity ofstabilizing agent employed.

These and other objects of this invention will be evident from thefollowing disclosure.

The method of this invention is applicable to polymers of lolefms havingtwo to eight carbon atoms per molecule, these including homopolymers ofethylene, propylene and the like and copolymers of related materials. Itis especially preferred in treating ethylene homopolymers and variouscopolymers of ethylene with other l-olefins such as propylene, l-buteneand the like. Such polymers are produced by a number of processesincluding those disclosed in U.S. Pat. No. 2,825,721 to Hogan et al.,and British Pat. No. 853,4l4. The method of this invention is applicableto these polymers as produced or containing additives conventionallyincluded such as colorants, plasticizers and the like.

The method of this invention is applicable to the addition of variousmelt flow stabilizers, both liquid and gaseous, such as halogens,nitrogen dioxide, sulfur dioxide, or any other effective melt flowstabilizer. While such stabilizers are known to be effective in and ofthemselves, the method of this invention improves their effectiveness byallowing their greater incorporation and retention within the polymer.

For example, introduction of such stabilizing agents by themselves isfrequently difficult because the moisture or air expelled y the e duringits prostateses itqr e eqt being sufficient to adsorb and hold the agentunder the conditions involved and permit incorporation of the agent to agreater extent than the agent would be adsorbed and held in the plasticin the absence of the carrier. Such materials include molecular sieves,such as sodium aluminum silicate and hydrated alumina, zeolites, andporous adsorbents in general.

The agent is incorporated in the adsorbent in any suitable manner.Generally, the adsorbent will be dried and activated at an elevatedtemperature and then contacted with the agent concerned for a suitablelength of time, preferably by passing the agent through a bed of theadsorbent until the adsorbent has adsorbed the desired quantity of theagent. The particle size of the adsorbent should be less than about l50microns and preferably less than 50 microns, and a pore size of fromabout 10 to about A.

The agent will be contained in the adsorbent in such quantities thatfrom about 0.001 to about 0.5 pound of agent is introduced per hundredpound of polymer. To effect this, about 0.01 to about 5 pounds ofagent-containing adsorbent will be incorporated in 100 pounds ofpolymer.

The agent-containing adsorbent can be incorporated in the polymer by anysuitable mixing method which produces its thorough and uniformdistribution. Mixing can be affected by Banbury and Brabender mixers,roll mills and the like, or by uniform introduction into an extruder.The incorporation of the agent-containing adsorbent into the polymer canbe made by mixing with the polymer in the dry state, preferably justprior to the thermal processing of the polymer, or while the polymer isin the molten state.

The following data indicate the effectiveness of the method of thisinvention when incorporating a melt index drop preventative agent in apolymer.

EXAMPLE I A sodium aluminum silicate adsorbent having a particle poresize of 10 A. and containing various weight percentages of NO wasincorporated in a polyethylene.

Melt flow values were determined on a polyethylene polymer at 550 F.under a load of 2,160 grams in terms of grams extruded per S-minuteperiod.

This temperature is higher than that temperature employed for thesedeterminations for polyethylene in accordance with ASTM Procedure Dl238-62T, Condition E. However, this higher temperature was employedsince the melt flow dropoff is more evident at this temperature with amelt flow dropoff of lesser magnitude being evident at the lowertemperature prescribed by the ASTM Testing procedure.

In Run 0, neither adsorbent nor NO was incorporated in the polymer whilein Run 3, only adsorbent alone was incorporated in the polymer. In theother runs, various quantities of both N0 and adsorbent wereincorporated in the polymer, the N0 being adsorbed in the adsorbent andthe resulting adsorbent being introduced into the polymer. Results wereas follows:

introduction of the agent into the polymer. Further, the retentiveproperties of the adsorbent allows incorporation of a greater proportionof the agent than would otherwise be possi- These data indicate theeffectiveness of the method of this invention in incorporating theagents concerned into a polymeric material when employing sodiumaluminum silicate ble, making the processing temperatures encounteredcon- 7 as the adsorbent.

siderably less effective in driving off the agent prior to itsincorporation in the polymer.

The adsorbents or carriers, the use of which are contemplated by thisinvention, include any material exhibiting an adsorption capacity forthe agent concerned, such capacity EXAMPLE u A similar set of runs wasmade employing N0 as the agent adsorbed in hydrated alumina having apore diameter of about Results were as follows:

60 A. Procedures were as described for Example I. Results were asfollows:

molecule which comprises contacting a porous adsorbent with said agentto produce an agent-containing adsorbent and in- These date indicate theeffectiveness of the method of this invention in incorporating theagents concerned in a polymeric material employing hydrated alumina asthe adsorbent.

ln order to illustrate the beneficial and unexpected improvement of thepresent method of introducing such agents over introducing the agentsinto the polymer in the absence of the adsorbents, the following runswere made.

EXAMPLE III A second polyethylene was subjected to melt flowdeterminations. NO was added to a second sample of the same polymer andmelt fiow values were determined. N was then incorporated in samples ofthe polymer employing two different adsorbents and melt flow valuesagain determined.

corporating said agent-containing adsorbent into said polymer in anamount sufficient to provide in said polymer from about 0.001 to about0.5 pound of said agent per 100 pounds of said polymer.

2. The method as defined in claim 1 in which said adsorbent is selectedfrom the group consisting of molecular sieves and zeolites.

3. The method as defined in claim 1 in which said adsorbent isintroduced into said polymer in an amount from about 0.01 to about 5pounds per 100 pounds of polymer.

4. The method as defined in claim 1 in which said adsorbent is activatedat elevated temperatures and purged with nitrogen prior to contactingwith said agent.

5. The method as defined in claim 1 in which said adsorbent has aarticle size of less than about 150 microns.

6. he method as defined in claim 1 in which said absorbent TABLE IIIAdsorbent Wt. percent Approx.

incorporated, N01 incor- Melt flow after overall Run \vt. percentporated in change,

No. of polymer polymer 5 min. min. min. min. percent 2 Hydrated aluminaincorporated in Runs 13, 18 and 19.

These data indicate the definite superiority of the method of has a poresize of from about 10 to about 60 A.

the present invention for the introduction of melt flow affectingagents. When incorporating the same quantity of the agent in the polymerin the absence of the adsorbent, the percentage change in the melt flowbetween the 5 and 20 minute points was about 2l to about 59 percent.When the agent was incorporated in the polymer in an adsorbent accordingto the method disclosed herein, this change was reduced to about 13 toabout 26 percent, depending upon the amount of the agent incorporated.

It will be noted that the foregoing data indicates that the method ofthis invention not only retards melt index dropoff but, in comparisonwith the melt index values of the untreated polymer, increases the meltindex of the polymer.

It will be evident from the above discussion that various modificationscan be made to the method of this invention. However, such modificationsare considered as being within the scope of this invention.

What is claimed is:

l. A method of incorporating a polymer melt flow stabilizing agent intoa polymer selected from homopolymers and copolymers of l-olefins havingtwo to eight carbon atoms per 7. The method as defined in claim 1 inwhich said adsorbent is incorporated into said polymer, said polymerbeing in the dry state.

8. The method as defined in claim 1 in which said adsorbent isincorporated into said polymer, said polymer being in the molten state.

9. The method as defined in claim 1 in which a sodium aluminum silicateis contacted with N0 to produce an N O -containing sodium aluminumsilicate and said sodium aluminum silicate is incorporated into apolyethylene polymer in an amount of from about 0.01 to about 5 ofadsorbent per pounds of polymer and in an amount sufficient to introducefrom about 0.001 to about 0.5 pounds of said agent per l00 pounds ofpolymer.

10. The method of claim 1 in which said polymer is polyethylene, saidstabilizing agent is N0 and said adsorbent is hydrated alumina, saidagent-containing adsorbent being incorporated in said polyethylene in anamount to provide in said polyethylene a hydrated alumina concentrationof about 4 weight percent and a N0 concentration of about 0.04 weightpercent.

2. The method as defined in claim 1 in which said adsorbent is selectedfrom the group consisting of molecular sieves and zeolites.
 3. Themethod as defined in claim 1 in which said adsorbent is introduced intosaid polymer in an amount from about 0.01 to about 5 pounds per 100pounds of polymer.
 4. The method as defined in claim 1 in which saidadsorbent is activated at elevated temperatures and purged with nitrogenprior to contacting with said agent.
 5. The method as defined in claim 1in which said adsorbent has a particle size of less than about 150microns.
 6. The method as defined in claim 1 in which said absorbent hasa pore size of from about 10 to about 60 A.
 7. The method as defined inclaim 1 in which said adsorbent is incorporated into said polymer, saidpolymer being in the dry state.
 8. The method as defined in claim 1 inwhich said adsorbent is incorporated into said polymer, said polymerbeing in the molten state.
 9. The method as defined in claim 1 in whicha sodium aluminum silicate is contacted with NO2 to produce anNO2-containing sodium aluminum silicate and said sodium aluminumsilicate is incorporated into a polyethylene polymer in an amount offrom about 0.01 to about 5 of adsorbent per 100 pounds of polymer and inan amount sufficient to introduce from about 0.001 to about 0.5 poundsof said agent per 100 pounds of polymer.
 10. The method of claim 1 inwhich said polymer is polyethylene, said stabilizing agent is NO2 andsaid adsorbent is hydrated alumina, said agent-containing adsorbentbeing incorporated in said polyethylene in an amount to provide in saidpolyethylene a hydrated alumina concentration of about 4 weight percentand a NO2 concentration of about 0.04 weight percenT.